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Ehrenfels B, Baumann KBL, Niederdorfer R, Mbonde AS, Kimirei IA, Kuhn T, Magyar PM, Odermatt D, Schubert CJ, Bürgmann H, Lehmann MF, Wehrli B, Callbeck CM. Hydrodynamic regimes modulate nitrogen fixation and the mode of diazotrophy in Lake Tanganyika. Nat Commun 2023; 14:6591. [PMID: 37852975 PMCID: PMC10584864 DOI: 10.1038/s41467-023-42391-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Accepted: 10/10/2023] [Indexed: 10/20/2023] Open
Abstract
The factors that govern the geographical distribution of nitrogen fixation are fundamental to providing accurate nitrogen budgets in aquatic environments. Model-based insights have demonstrated that regional hydrodynamics strongly impact nitrogen fixation. However, the mechanisms establishing this physical-biological coupling have yet to be constrained in field surveys. Here, we examine the distribution of nitrogen fixation in Lake Tanganyika - a model system with well-defined hydrodynamic regimes. We report that nitrogen fixation is five times higher under stratified than under upwelling conditions. Under stratified conditions, the limited resupply of inorganic nitrogen to surface waters, combined with greater light penetration, promotes the activity of bloom-forming photoautotrophic diazotrophs. In contrast, upwelling conditions support predominantly heterotrophic diazotrophs, which are uniquely suited to chemotactic foraging in a more dynamic nutrient landscape. We suggest that these hydrodynamic regimes (stratification versus mixing) play an important role in governing both the rates and the mode of nitrogen fixation.
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Affiliation(s)
- Benedikt Ehrenfels
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Surface Waters - Research and Management, Kastanienbaum, Switzerland
- ETH Zurich, Institute of Biogeochemistry and Pollutant Dynamics, Zurich, Switzerland
| | - Kathrin B L Baumann
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Surface Waters - Research and Management, Kastanienbaum, Switzerland
- ETH Zurich, Institute of Biogeochemistry and Pollutant Dynamics, Zurich, Switzerland
| | - Robert Niederdorfer
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Surface Waters - Research and Management, Kastanienbaum, Switzerland
| | | | - Ismael A Kimirei
- TAFIRI, Tanzania Fisheries Research Institute, Kigoma, Tanzania
- TAFIRI, Tanzania Fisheries Research Institute, Dar es Salaam, Tanzania
| | - Thomas Kuhn
- University of Basel, Department of Environmental Sciences, Basel, Switzerland
| | - Paul M Magyar
- University of Basel, Department of Environmental Sciences, Basel, Switzerland
| | - Daniel Odermatt
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Surface Waters - Research and Management, Kastanienbaum, Switzerland
| | - Carsten J Schubert
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Surface Waters - Research and Management, Kastanienbaum, Switzerland
- ETH Zurich, Institute of Biogeochemistry and Pollutant Dynamics, Zurich, Switzerland
| | - Helmut Bürgmann
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Surface Waters - Research and Management, Kastanienbaum, Switzerland
| | - Moritz F Lehmann
- University of Basel, Department of Environmental Sciences, Basel, Switzerland
| | - Bernhard Wehrli
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Surface Waters - Research and Management, Kastanienbaum, Switzerland
- ETH Zurich, Institute of Biogeochemistry and Pollutant Dynamics, Zurich, Switzerland
| | - Cameron M Callbeck
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department Surface Waters - Research and Management, Kastanienbaum, Switzerland.
- University of Basel, Department of Environmental Sciences, Basel, Switzerland.
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Gruber W, Magyar PM, Mitrovic I, Zeyer K, Vogel M, von Känel L, Biolley L, Werner RA, Morgenroth E, Lehmann MF, Braun D, Joss A, Mohn J. Tracing N 2O formation in full-scale wastewater treatment with natural abundance isotopes indicates control by organic substrate and process settings. Water Res X 2022; 15:100130. [PMID: 35287381 PMCID: PMC8917317 DOI: 10.1016/j.wroa.2022.100130] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Revised: 02/25/2022] [Accepted: 02/26/2022] [Indexed: 06/14/2023]
Abstract
Nitrous oxide (N2O) dominates greenhouse gas emissions in wastewater treatment plants (WWTPs). Formation of N2O occurs during biological nitrogen removal, involves multiple microbial pathways, and is typically very dynamic. Consequently, N2O mitigation strategies require an improved understanding of nitrogen transformation pathways and their modulating controls. Analyses of the nitrogen (N) and oxygen (O) isotopic composition of N2O and its substrates at natural abundance have been shown to provide valuable information on formation and reduction pathways in laboratory settings, but have rarely been applied to full-scale WWTPs. Here we show that N-species isotope ratio measurements at natural abundance level, combined with long-term N2O monitoring, allow identification of the N2O production pathways in a full-scale plug-flow WWTP (Hofen, Switzerland). Heterotrophic denitrification appears as the main N2O production pathway under all tested process conditions (0-2 mgO2/l, high and low loading conditions), while nitrifier denitrification was less important, and more variable. N2O production by hydroxylamine oxidation was not observed. Fractional N2O elimination by reduction to dinitrogen (N2) during anoxic conditions was clearly indicated by a concomitant increase in site preference, δ18O(N2O) and δ15N(N2O). N2O reduction increased with decreasing availability of dissolved inorganic N and organic substrates, which represents the link between diurnal N2O emission dynamics and organic substrate fluctuations. Consequently, dosing ammonium-rich reject water under low-organic-substrate conditions is unfavorable, as it is very likely to cause high net N2O emissions. Our results demonstrate that monitoring of the N2O isotopic composition holds a high potential to disentangle N2O formation mechanisms in engineered systems, such as full-scale WWTP. Our study serves as a starting point for advanced campaigns in the future combining isotopic technologies in WWTP with complementary approaches, such as mathematical modeling of N2O formation or microbial assays to develop efficient N2O mitigation strategies.
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Affiliation(s)
- Wenzel Gruber
- Eawag, Swiss Federal Institute for Aquatic Science and Technology, 8600 Dübendorf, Switzerland
| | - Paul M Magyar
- Department of Environmental Sciences, Aquatic and Isotope Biogeochemistry, University of Basel, Basel 4056, Switzerland
| | - Ivan Mitrovic
- Eawag, Swiss Federal Institute for Aquatic Science and Technology, 8600 Dübendorf, Switzerland
| | - Kerstin Zeyer
- Laboratory for Air Pollution / Environmental Technology, Empa, Dübendorf 8600, Switzerland
| | - Michael Vogel
- Department of Civil, Environmental and Geomatic Engineering, ETH, Zürich 8093, Switzerland
| | - Luzia von Känel
- Department of Civil, Environmental and Geomatic Engineering, ETH, Zürich 8093, Switzerland
| | - Lucien Biolley
- Department of Civil, Environmental and Geomatic Engineering, ETH, Zürich 8093, Switzerland
| | - Roland A Werner
- Department of Environmental Systems Science, ETH, Zürich 8092, Switzerland
| | - Eberhard Morgenroth
- Eawag, Swiss Federal Institute for Aquatic Science and Technology, 8600 Dübendorf, Switzerland
| | - Moritz F Lehmann
- Department of Environmental Sciences, Aquatic and Isotope Biogeochemistry, University of Basel, Basel 4056, Switzerland
| | - Daniel Braun
- Department of Civil, Environmental and Geomatic Engineering, ETH, Zürich 8093, Switzerland
| | - Adriano Joss
- Eawag, Swiss Federal Institute for Aquatic Science and Technology, 8600 Dübendorf, Switzerland
| | - Joachim Mohn
- Laboratory for Air Pollution / Environmental Technology, Empa, Dübendorf 8600, Switzerland
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Magyar PM, Orphan VJ, Eiler JM. Measurement of rare isotopologues of nitrous oxide by high-resolution multi-collector mass spectrometry. Rapid Commun Mass Spectrom 2016; 30:1923-1940. [PMID: 27501428 DOI: 10.1002/rcm.7671] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Revised: 06/16/2016] [Accepted: 06/18/2016] [Indexed: 06/06/2023]
Abstract
RATIONALE Bulk and position-specific stable isotope characterization of nitrous oxide represents one of the most powerful tools for identifying its environmental sources and sinks. Constraining (14) N(15) N(18) O and (15) N(14) N(18) O will add two new dimensions to our ability to uniquely fingerprint N2 O sources. METHODS We describe a technique to measure six singly and doubly substituted isotopic variants of N2 O, constraining the values of δ(15) N, δ(18) O, ∆(17) O, (15) N site preference, and the clumped isotopomers (14) N(15) N(18) O and (15) N(14) N(18) O. The technique uses a Thermo MAT 253 Ultra, a high-resolution multi-collector gas source isotope ratio mass spectrometer. It requires 8-10 hours per sample and ~10 micromoles or more of pure N2 O. RESULTS We demonstrate the precision and accuracy of these measurements by analyzing N2 O brought to equilibrium in its position-specific and clumped isotopic composition by heating in the presence of a catalyst. Finally, an illustrative analysis of biogenic N2 O from a denitrifying bacterium suggests that its clumped isotopic composition is controlled by kinetic isotope effects in N2 O production. CONCLUSIONS We developed a method for measuring six isotopic variants of N2 O and tested it with analyses of biogenic N2 O. The added isotopic constraints provided by these measurements will enhance our ability to apportion N2 O sources.
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Affiliation(s)
- Paul M Magyar
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Victoria J Orphan
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA
| | - John M Eiler
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, 91125, USA
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